DNA hybridization techniques have been used to detect endogenous genes in various primates which are related to the three known families of Old World primate viruses, and to quantitate their evolution. Comparisons of the evolutionary patterns of these viral genes suggests that their evolutionary divergence is sufficiently great that viral genes from one of the apes will be necessary in order to study human endogenous genes. One effects to develop probes specific to various regions of the viral genome now focus on developing a restriction enzyme map of the genome and cloning of the viral genomes using recombinant DNA techniques. We have begun attempts to determine the chromosomal location of the M28 and MAC-1 viral sequences in the chimpanzee.